This invention relates to an erosion resistant electrostatic chuck for holding substrates in process chambers.
In semiconductor fabrication processes, electrostatic chucks are used to hold substrates, such as silicon wafers, during processing of the substrate. Electrostatic chucks are generally described in, for example, U.S. Pat. No. 4,399,016, to Tokuda; U.S. Pat. No. 4,384,918, to Abe; and U.S. patent application Ser. No. 08/189,562, entitled "Electrostatic Chuck" by Shamouilian, et al., filed on Jan. 31, 1994--all of which are incorporated herein by reference.
A typical electrostatic chuck comprises a base adapted to be secured to a support in a process chamber. An electrostatic member is on the base, the electrostatic member typically comprising an insulator with an electrode therein. An insulated electrical connector extends over the edge of the base, and connects the electrostatic member on the base to a high voltage supply in the process chamber. The electrical connector is typically insulated by an insulative polymer, such as polyimide.
During its use, the chuck is secured to a support in the process chamber. A substrate is placed on the chuck, and the electrostatic member of the chuck is electrically biased with respect to the substrate by an electrical voltage applied by a voltage source in the process chamber. Electrostatic charge accumulates in the electrostatic member of the chuck and on the substrate, and the resultant electrostatic force holds the substrate to the chuck.
The use of polymers, such as polyimides, to insulate the electrical connector of the chuck limits the lifetime of the chuck in corrosive semiconductor fabrication processes, particularly in processes using oxygen containing gases and plasmas. Oxygen containing gases and plasmas are used for a variety of tasks, including for the etching of substrates and cleaning of process chamber walls. These corrosive environments rapidly erode the exposed portions of the electrical connector of the chuck, which extend along the edge of the chuck. The exposed portions of the electrical connector can erode in as few as a thousand process cycles.
Erosion of the electrical connector at even a single point is sufficient to cause arcing between the electrode and the plasma, resulting in failure of the chuck, and requiring replacement of the entire chuck. Frequent replacement of chucks is expensive and slows down the fabrication process. Also, if the chuck fails during processing of the substrate, the entire substrate can be lost, at a cost of several thousands of dollars.
Although alternative insulators, such as silicon oxide based insulators, can be used to protect chucks from oxygen containing processes, these materials have other inherent limitations. For example, silicon oxide based insulators rapidly corrode in processes that use fluorine containing gases, such as fluorocarbon gases. Also, silicon oxide based insulators are more difficult and expensive to manufacture.
Thus, it is desirable to have electrostatic chuck that is substantially resistant to erosion in erosive gaseous environments. It is further desirable to have a chuck that can be inexpensively fabricated using conventional fabrication equipment.